1. Field of the Invention
The present invention relates to a novel curable composition, a thermal latent acid catalyst, a method of coating, a coated article, a method of molding and a molded article. More particularly, it relates to a novel curable composition which is particularly excellent in storage stability and gives cured products having excellent chemical properties, physical properties, weathering resistance and stain resistance, which is able to be utilized in the field of coatings, ink, adhesive and molded plastics, a thermal latent catalyst capable to be utilized in the thermosetting composition, and a method of coating to provide a top coat having the above cured film properties and excellent appearance by using the curable composition as the top coat material and the obtained coated article. It also relates to a method of molding to provide a molded article having excellent mechanical properties, insulating characteristics, moisture resistance, corrosion resistance and cracking resistance by using the curable composition as the molding material and the obtained molded article.
2. Description of the Prior Art
It is generally known that thermosetting compositions can be prepared from compounds having carboxyl groups and compounds having reactive functional groups which can form chemical bonds with the carboxyl groups by heating, such as epoxy group, oxazoline group, silanol group, alkoxysilane group, hydroxyl group, amino group, imino group, isocyanate group, blocked isocyanate group, cyclocarobonate group, vinyl ether group, vinyl thioether group, aminomethylol group, alkylated aminomethylol group, acetal group and ketal group. The thermosetting compositions give cured products having excellent chemical properties, physical properties and weathering resistance and are widely utilized in the field of coating composition, ink, adhesive and molded plastics.
As the thermosetting compositions described above, for example, compositions comprising combinations of carboxyl group and epoxy group have been disclosed in Laid Open Japanese Patent Application Showa 51-114429, Laid Open European Patent Application 29595 and U.S. Pat. Nos. 4,371,667, 4,650,718, 4,681,811, 4,703,101 and 4,764,430.
However, the reactivity between the carboxyl group and the reactive functional groups is generally very high so that compositions in which compounds having carboxyl groups and compounds having the reactive functional groups are mixed together have a problem that the compositions are often gelled during storage and the period suitable for pot life is short.
Compounds comprising carboxyl groups conventionally utilized for thermosetting compositions described above have problems that solubility to generally used solvents is low and that compatibility with the compounds having reactive groups with the carboxyl group is inferior because of the tendency of the carboxyl group to form strong hydrogen bonds. When thermosetting compositions comprising these kinds of compounds are utilized as top coat materials, they naturally have problems that preparation of high solid coating materials which discharge a small amount of organic solvents into air during coating is difficult and that appearance of the finished coating is inferior. Furthermore, when the thermosetting compositions are utilized as molding materials, they naturally have problems that defects such as bubbles and cavities are easily caused in the molded articles by a great deal of volatile organic compounds.
For the purpose of solving these problems, it was proposed that the carboxyl group was blocked by converting it to tertiary-butyl ester and the ester was decomposed by heating, and the free carboxyl group was regenerated by elimination of isobutene (Laid Open Japanese Patent Application Heisei 1-104646).
However, there was a problem that this method required a high temperature, such as 170-200.degree. C., for the heat decomposition of the tertiary-butyl ester. Thus, this method is not sufficiently satisfactory in view of economy in resources and energy. Furthermore, pock marks which were made by foaming and degassing of isobutene formed by the decomposition remained on the cured surface of the coating.
It is also generally known that two component compositions can be prepared by mixing isocyanate group-containing compounds and hydroxyl group-containing compounds, as a curable composition at lower temperatures which can produce cured products at a near room temperature.
The compositions, however, have a problem that preparation of high solid coating materials is difficult, because the compositions essentially comprise compounds containing a great deal of hydroxyl groups having a high ability to form hydrogen bonds.